Timed practice is frustrating

As native german speaker trying to learn portuguese i find "Timed Practice" very frustrating because i am not able to type 10 to 15 word sentences in english or portuguese fast enough. These long exercises should be filtered or given more time to answer.

as an optimization freak i already follow most of these rules but still with no luck, the upper portuguese levels only seem to contain sentences with 10 or more words. it's also the total lack of consistency (i.e. vou - eu vou) which drives me crazy...

I think you took it the wrong way. The timed practice helps me remember quickly and commit it to memory. If you're taking time to write it, then it probably either means you can't remember it well, or you type slowly. These circumstances are what untimed practice is for I guess.

Big sentences I also struggle with in french, I tend to just skip them completely if i can't recall a word or two.

Well I'm not a native English speaker, yet I can keep up. I think the problem is that you expect it to give you as much time as possible. I see it more as a way to quickly find out which words and sentences I know, and skip the rest for untimed practice.

The problem is that despite the advice given by Dessamator below you are FAILED if you miss an accent in the timed test - the time allowed is WAY too short unless you are a professional typist... (do they still exist??)